Chilean Earthquake Restores Beaches

EMERALD LAKES, TONGARIRO, NEW ZEALAND Near the summit of Mount Tongariro in New Zealand's volcanic region, the Emerald Lakes take their color partly from dissolved minerals. Courtesy of Antoine Hubert

CRATER LAKE, OREGON About 6,850 years ago, Mount Mazama blew its top in a massive explosion that rained ash, dust and lava. Following the explosion, Mazama's top collapsed to form the caldera you see in this shot, taken in 2006 from the International Space Station. The caldera later filled with water and became what is now one of the world's largest freshwater lakes with the deepest average depth of any in North America. Courtesy of NASA

KILAUEA CALDERA, HAWAII One of the world's most active volcanoes, Kilauea harbors a summit caldera that is covered in fresh lava flows in this satellite image. Courtesy of IKONOS/NASA

SANTA ANA VOLCANO, EL SALVADOR Look closely to spot two lakes in this colorized satellite image. The first, a crater lake, appears as a tiny blue area at the summit of the Santa Ana volcano, the highest point in El Salvador. The second, just behind and to the right of Santa Ana, is a much larger caldera lake inside the Coatepeque Caldera. The red coloring indicates vegetation on the slopes of the volcanoes. Courtesy Robert Simmon based on data provided by Timothy Gubbels and Asad Ullah/SSAI/NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team

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CRATER LAKE, RUAPEHU, NEW ZEALAND The pale blue dot in the center of this image marks Crater Lake atop New Zealand's Mount Ruapehu, one of the most thoroughly studied and monitored volcanic lakes in the world. "Eruptions through the lake occur relatively frequently, changing the physical dimensions of the lake and posing a constant threat to human activities in the area," scientists at the University of California, Davis, wrote. NASA image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

In 2010, a massive, magnitude-8.8 earthquake struck the south central coast of Chile, rupturing beaches and launching a tsunami that rode inland with devastating effect. In an instant, whole sections of the coastline were transformed, with large swaths of sand and rock lifted from beneath the waves.

For Chile, it was a disaster of sobering proportions. But for Eduardo Jaramillo and Jenifer Dugan -- researchers who have spent years studying the effects of coastal erosion on beach ecology -- it was also a rare opportunity to see one of climate change's more immediate effects put in reverse.

"It was like setting the clock backward," said Dugan, a researcher at the Marine Science Institute of the University of California, Santa Barbara. "The whole coast went up in places. Beaches that had been much lower elevation relative to sea level came up a couple of meters. They regained a lot of lost ground."

Before the quake, that "lost ground" had been steadily eaten away by a combination of natural and human influences.

As thermal expansion and glacial melt -- both products of global climate change -- push sea levels steadily higher, coastlines are shifting inland. Yet in many places, that shift has been arrested by man-made sea walls, vast projects meant to protect the trillions of dollars of infrastructure that perch on the edge of the world's oceans.

Sea walls are often constructed at high-tide lines, and although they may protect the infrastructure behind them, they actually exacerbate the erosion of the beach in front of them, said Jaramillo, of Universidad Austral de Chile.

How sea walls accelerate erosion
"When you build a sea wall close to high tide, the water actually hits it and bounces off with more force" than if the tide had been allowed to go out naturally, he said. Beaches lose more sand to erosion when they have sea walls than when they're allowed to move naturally, he added.

For the plants and animals that inhabit beaches, that means a precipitous loss of habitat. Along much of the Chilean coast, species have abandoned beaches hemmed in by closing walls of water and concrete. But in those places where the quake lifted new ground, life quickly returned.

"Dune plants are coming back in places there haven't been plants, as far as we know, for a very long time," Dugan said. "The earthquake created sandy beach habitat where it had been lost." Invertebrate and avian life were coming back quickly, as well, she said.

"This is not the initial ecological response you might expect from a major earthquake and tsunami," she added.

Jaramillo said their findings highlighted the damage sea walls could do to coastal ecology, adding that they should inform future policy. Sandy beaches are in many ways a better buffer against tides, because they extend into the ocean and absorb shock gradually, he added.

By contrast, sea walls expedite the erosion of the beach, so that when, eventually, there is no buffer left, the ocean's tides strike with greater force -- increasing the likelihood that, should the sea wall break, the area behind it will be more severely affected, he said.

The researchers' findings were published last week in the online journal PLoS ONE.

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